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.Dd January 15, 2017
.Dt DEVICE 9
.Os
.Sh NAME
.Nm device
.Nd an abstract representation of a device
.Sh SYNOPSIS
.Vt typedef struct _device *device_t ;
.Sh DESCRIPTION
The device object represents a piece of hardware attached to the
system such as an expansion card, the bus which that card is plugged
into, disk drives attached to the expansion card etc.
The system defines one device,
.Va root_bus
and all other devices are created dynamically during
autoconfiguration.
Normally devices representing top-level buses in
the system (ISA, PCI etc.) will be attached directly to
.Va root_bus
and other devices will be added as children of their relevant bus.
.Pp
The devices in a system form a tree.
All devices except
.Va root_bus
have a parent (see
.Xr device_get_parent 9 ) .
In addition, any device can have children attached to it (see
.Xr device_add_child 9 ,
.Xr device_add_child_ordered 9 ,
.Xr device_find_child 9 ,
.Xr device_get_children 9 ,
and
.Xr device_delete_child 9 ) .
.Pp
A device which has been successfully probed and attached to the
system will also have a driver (see
.Xr device_get_driver 9
and
.Xr driver 9 )
and a devclass (see
.Xr device_get_devclass 9
and
.Xr devclass 9 ) .
Various other attributes of the device include a unit number (see
.Xr device_get_unit 9 ) ,
verbose description (normally supplied by the driver, see
.Xr device_set_desc 9
and
.Xr device_get_desc 9 ) ,
a set of bus-specific variables (see
.Xr device_get_ivars 9 )
and a set of driver-specific variables (see
.Xr device_get_softc 9 ) .
.Pp
Devices can be in one of several states:
.Bl -tag -width DS_NOTPRESENT
.It Dv DS_NOTPRESENT
the device has not been probed for existence or the probe failed
.It Dv DS_ALIVE
the device probe succeeded but not yet attached
.It Dv DS_ATTACHED
the device has been successfully attached
.It Dv DS_BUSY
the device is currently open
.El
.Pp
The current state of the device can be determined by calling
.Xr device_get_state 9 .
.Sh SEE ALSO
.Xr devclass 9 ,
.Xr driver 9
.Sh AUTHORS
This manual page was written by
.An Doug Rabson .
